There is no way that the synthetic will pack as small or be as light. For example, my 20° SLD UQ can get stuffed into a 20lt compression dry bag, but I can put both of my 40° down quilts into a 14lt w/ room to spare. Of course my 40° UQ is short (only 50" long) but even full length it would still go in.
The thought is that synthetic can resist loosing it’s heat retention even if a bit damp where down can not, BUT there is now several venders using treated down that resists getting wet.
As far as UGQ, I love the custom TQ I got but as far as an UQ I’m not sold on the “taco” style UQs. After using SLDs UQ all winter I really like that style of UQ. Of course he doesn’t use down. So now I’m looking at possibly modding my short down Loco Libre summer quilt by adding it to one of SLDs UQ protectors (UQP) that I already have.
I picked up that shorty for summer bike & backpacking because it’s so small.
So for me I think the SLD if you have the room and weight isn’t the biggest issue, or Warbonnets Wookie if you lay the same way always when in the hammock and want down, are my preferred style of UQ. Super simple, min adjustments, no air gaps.
If I’d known how much I don’t like having the suspension lines from a short quilt running up near my face I’d have gone w/ a different option, but then modding things has never been a problem for me.